WM_CLOSE:关闭应用程序窗口
WM_DESTROY:关闭应用程序
WM_QUIT:关闭消息循环
只有关闭了消息循环,应用程序的进程才真正退出(在任务管理器里消失)。
win32应用程序的完整退出过程:点击窗口右上角的关闭按钮,发送WM_CLOSE消息。此消息处理中调用DestroyWindow函数,发送WM_DESTROY消息。此消息处理中调用PostQuitMessage(0)函数,发送WM_QUIT消息到消息队列中。GetMessage捕获到WM_QUIT,返回0,退出循环(应用程序真正退出)。
tips:按照上述正常流程,WM_QUIT是不会到达窗口过程的。(因为在GetMessage截获了WM_QUIT消息之后,程序已经彻底退出了!)
MFC应用程序的完整退出过程:点击窗口右上角的关闭按钮,或选择【File/Close】,发出 WM_CLOSE消息。CMyFrameWnd 并没有设置WM_CLOSE 处理常式,于是交给预设之处理常式。预设函数对于WM_CLOSE 的处理方式是呼叫 ::DestroyWindow, 并因而发出WM_DESTROY。预设之WM_DESTROY 处理方式是呼叫::PostQuitMessage,因此发出WM_QUIT。CWinApp::Run 收到WM_QUIT 后会结束其内部之讯息回路, 然后呼叫ExitInstance,这是CWinApp 的?个虚拟函数。如果自己应用程序累CMyWinApp 改写了ExitInstance , 那么CWinApp::Run 所呼叫的就是CMyWinApp::ExitInstance,否则就是 CWinApp::ExitInstance。最后回到 AfxWinMain,执行 AfxWinTerm,结束程序。
附加:当调用DestroyWindow函数后,操作系统就会进行一系列的删除动作,先发送WM_DESTROY消息,接着发送WM_NCDESTROY消息。如果这个窗口还有子窗口或者是其它窗口的所有者,就需要给所有子窗口发送删除消息。
WM_QUIT是唯一可以使GetMessage(&msg,NULL,0,0)返回假值的消息.
相关代码分析:
//主函数中进入消息循环的代码片断
while(GetMessage(&msg,NULL,0,0))
{
TranslateMessage(&msg); //将消息进行处理一下
DispatchMessage(&msg); //再将消息变量msg传给windows,让windows来调用消息处理函数
}
如果把GetMessage(&msg,NULL,0,0)改为GetMessage(&msg,hWnd,0,0),则发现关闭应用程序后,任务管理器中仍有该程序的进程,且占用大量的内存,why?
msdn中的原因解释;对于GetMessage(&msg,hWnd,0,0),当第二个参数无效时,此函数返回值为-1。对于上述循环来说,此while条件为真,因此进入死循环,进程无法退出。
http://hhfighting.blog.163.com/blog/static/5570032320108215323797/
---------------------------------------------------------------------------------------------------------------
VCL里相应的代码:
procedure TCustomForm.WMClose(var Message: TWMClose); begin Close; end; procedure TCustomForm.Close; var CloseAction: TCloseAction; begin if fsModal in FFormState then ModalResult := mrCancel else if CloseQuery then begin if FormStyle = fsMDIChild then if biMinimize in BorderIcons then CloseAction := caMinimize else CloseAction := caNone else CloseAction := caHide; DoClose(CloseAction); if CloseAction <> caNone then if Application.MainForm = Self then Application.Terminate else if CloseAction = caHide then Hide else if CloseAction = caMinimize then WindowState := wsMinimized else Release; end; end; procedure TCustomForm.WMDestroy(var Message: TWMDestroy); begin if NewStyleControls then SendMessage(Handle, WM_SETICON, 1, 0); if (FMenu <> nil) and (FormStyle <> fsMDIChild) then begin Windows.SetMenu(Handle, 0); FMenu.WindowHandle := 0; end; inherited; end;
还有:
function TApplication.ProcessMessage(var Msg: TMsg): Boolean; var Handled: Boolean; begin Result := False; if PeekMessage(Msg, 0, 0, 0, PM_REMOVE) then begin Result := True; if Msg.Message <> WM_QUIT then begin Handled := False; if Assigned(FOnMessage) then FOnMessage(Msg, Handled); if not IsHintMsg(Msg) and not Handled and not IsMDIMsg(Msg) and not IsKeyMsg(Msg) and not IsDlgMsg(Msg) then begin TranslateMessage(Msg); DispatchMessage(Msg); end; end else FTerminate := True; end; end;
DestroyWindow函数来自这里(TApplication.Destroy里也调用了这个函数):
procedure TWinControl.DestroyWindowHandle; begin Include(FControlState, csDestroyingHandle); try if not Windows.DestroyWindow(FHandle) then RaiseLastOSError; finally Exclude(FControlState, csDestroyingHandle); end; FHandle := 0; end;
那难道每个TButton,每个TPanel,都会收到WM_DESTROY消息吗?